Dies are widely used to cut variety of patterns on a workpiece, however, there are number of shortcomings with the use of a die. For example, individual dies must be custom made for a specific cut requirement, which can be very expensive. Also, after a period of cutting, dies must be retooled or replaced as they get worn-out. Consequently, during the life of a die, the quality of the cuts made by the die degenerates, thus producing inconsistent qualities of cuts over that period of time. Productivity may also be limited because under some circumstances, before a die can cut into a workpiece, the workpiece must be stopped.
Another consequence of die-cutting is a formation of dust surrounding the die-cutting area. This dust is formed because dies are designed to cut almost through the web, instead of all the way through, thereby leaving the bottom-most area uncut. Consequently, the bottom-most area because of its weakness breaks off, which ultimately separates that sheet from the web. However, when the bottom-most area breaks off, fiber residue is created forming the dust. One of the reasons for not having the die cut all the way through is to prevent the upper die from bearing against the hard surface of the lower mating die. Thus, formation of the dust is inherent with the die-cutting, which is problematic for the press and the operators nearby working on the press. Additionally, the lack of close tolerance of a die makes it difficult to cut partially through the workpiece, i.e. control the depth of the cut on the workpiece.
Another shortcoming with the die-cutting is the scrap or waste, which is produced during the initial start up and shut down. Rotary dies, for example, requires the press to run at a defined speed, in order to cut properly. The speed of the press, however, accelerates during the period of start up and decelerates during the period of shut down. Accordingly, during the periods of startup and shutdown, the quality of the die cuts are inconsistent and much scrap is produced.
Furthermore, since a die can only cut one particular configuration at a time, production process may be limited. For example, sets of index tab sheets are generally manufactured by employing a die-cutting mechanism, which cuts one particular tab location from a pile of sheets. Thereafter, dies are adjusted or changed so that another pile of sheets are cut with the next index tab location. This process is repeated until all of the index tab sheets forming a set have been cut. After all the stacks of individual index tab sheets forming a set have been cut, they have to be collated in the right tab order for packaging, i.e. individual tab sheets must be pulled from each stacks and organized sequentially into a set. This additional step is both time consuming and labor intensive, and at the same time, taking up valuable manufacturing floor space to store the stacks of index tab sheets.
Others have employed laser beams to cut on a moving web to alleviate some of the shortcomings of the die-cutting process. For example, U.S. Pat. No. 5,679,199 to Nedblake et al., describes an upper and lower laser beams, which are shiftable in the Y axis (vertical) in order to cut through a web to form patterns as the web moves past the laser beams.
U.S. Pat. No. 4,549,063 to Ang et al., describes a system that has a plurality of lasers cutting on a moving web. The disclosed system also controls the depth of the cuts by regulating the relative velocity of the beam and the web, the power output of the laser, and the diameter of the focused spot of the laser, or a combination of these.
U.S. Pat. No. 4,049,945 to Ehlscheid et al., describes a method and apparatus for cutting a predetermined pattern on a moving web wherein a laser beam is deflected by a series of pivotable mirrors. These mirrors are controlled so as to cause the laser beam to trace and cut a predetermined pattern. The laser beam moves only in rectilinear motion, as does the web of material to be cut. The direction of motions are not parallel, so that a desired pattern may be cut by controlling the relative speeds of the laser beam and the moving web of material.
The laser cutting systems, as described above, still have a number of shortcomings. For instances, using a laser, as described above, to cut the sets of index tab sheets would still require a separate collating process. Also, using laser beams to cut a moving web creates its own set of problems. These problems include the vapors which are formed when a laser beam is used to cut a moving web, creating mechanical problems for the apparatus and dangerous working condition for the operators. Also the inherent nature of the prior laser cutting system creates extremely sharp edges, which may cause "paper cuts" for the users, as they come into contact with the sharp edges. Furthermore, normal operation of the press in the prior systems creates disturbances on the moving web causing laser to cut inaccurately on the moving web. Additionally, none of the above patents disclose a method in which the controller keeps track of the exact horizontal and vertical location of the moving web so that the laser may be directed to cut on the precise location of the moving web.
For the foregoing reasons, there is a need for a dynamic laser cutting apparatus that may interface with commercial web press, for cutting a variety of configurations on the moving web with precision, without the aforementioned shortcomings.